<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>Document</title>
        <style>
            
            .box {
                width: 600px;
                border: 2px solid black;
                float: left;
            }

            .a {
                width: 300px;
                height: 300px;
                background: red;
                clear: both;
            }

            .in {
                width: 200px;
                height: 200px;
                background: orange;
                float: right;
            }

            .clear::after {
                content: "";
                display: block;
                clear: both;
            }

        </style>
    </head>
    <body>
        
        <div class="box">
            <div class="in"></div>
        </div>
        <div class="a"></div>

        
    </body>
</html>